[FFmpeg-devel] [PATCH] ismindex: handle discontinuous streams better

[Mika Raento]

On 8 October 2014 08:12, Mika Raento <mikie at iki.fi> wrote:
> Reads the fragment duration from the trun sample data, rather than
> assuming that there are no gaps. Creates much better playlists for our
> inputs.
> ---
>  tools/ismindex.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 85 insertions(+), 11 deletions(-)
>
> diff --git a/tools/ismindex.c b/tools/ismindex.c
> index 734419b..dcbc115 100644
> --- a/tools/ismindex.c
> +++ b/tools/ismindex.c
> @@ -50,6 +50,7 @@
>  #include "cmdutils.h"
>
>  #include "libavformat/avformat.h"
> +#include "libavformat/isom.h"
>  #include "libavformat/os_support.h"
>  #include "libavutil/intreadwrite.h"
>  #include "libavutil/mathematics.h"
> @@ -226,6 +227,78 @@ fail:
>      return ret;
>  }
>
> +static int64_t read_trun_duration(AVIOContext *in, int64_t end)
> +{
> +    int64_t ret = 0;
> +    int64_t pos;
> +    int flags, i;
> +    int entries;
> +    avio_r8(in); /* version */
> +    flags = avio_rb24(in);
> +    if (! (flags & MOV_TRUN_SAMPLE_DURATION)) {
> +        fprintf(stderr, "no sample duration in trun flags");
> +        return -1;
> +    }
> +    entries = avio_rb32(in);
> +
> +    if (flags & MOV_TRUN_DATA_OFFSET) avio_rb32(in);
> +    if (flags & MOV_TRUN_FIRST_SAMPLE_FLAGS) avio_rb32(in);
> +
> +    pos = avio_tell(in);
> +    for (i = 0; i < entries && pos < end; i++) {
> +        int sample_duration = 0;
> +        if (flags & MOV_TRUN_SAMPLE_DURATION) sample_duration = avio_rb32(in);
> +        if (flags & MOV_TRUN_SAMPLE_SIZE) avio_rb32(in);
> +        if (flags & MOV_TRUN_SAMPLE_FLAGS) avio_rb32(in);
> +        if (flags & MOV_TRUN_SAMPLE_CTS) avio_rb32(in);
> +        if (sample_duration < 0) {
> +            fprintf(stderr, "negative sample duration %d\n", sample_duration);
> +            return -1;
> +        }
> +        ret += sample_duration;
> +        pos = avio_tell(in);
> +    }
> +
> +    return ret;
> +}
> +
> +static int64_t read_moof_duration(AVIOContext *in, int64_t offset)
> +{
> +    int64_t ret = -1;
> +    int32_t moof_size, size, tag;
> +    int64_t pos = 0;
> +
> +    avio_seek(in, offset, SEEK_SET);
> +    moof_size = avio_rb32(in);
> +    tag  = avio_rb32(in);
> +    if (expect_tag(tag, MKBETAG('m', 'o', 'o', 'f')) != 0) goto fail;
> +    while (pos < offset + moof_size) {
> +        pos = avio_tell(in);
> +        size = avio_rb32(in);
> +        tag  = avio_rb32(in);
> +        if (tag == MKBETAG('t', 'r', 'a', 'f')) {
> +            int64_t traf_pos = pos;
> +            int64_t traf_size = size;
> +            while (pos < traf_pos + traf_size) {
> +                pos = avio_tell(in);
> +                size = avio_rb32(in);
> +                tag  = avio_rb32(in);
> +                if (tag == MKBETAG('t', 'r', 'u', 'n')) {
> +                    return read_trun_duration(in, pos + size);
> +                }
> +                avio_seek(in, pos + size, SEEK_SET);
> +            }
> +            fprintf(stderr, "couldn't find trun");
> +            goto fail;
> +        }
> +        avio_seek(in, pos + size, SEEK_SET);
> +    }
> +    fprintf(stderr, "couldn't find traf");
> +
> +fail:
> +    return ret;
> +}
> +
>  static int read_tfra(struct Tracks *tracks, int start_index, AVIOContext *f)
>  {
>      int ret = AVERROR_EOF, track_id;
> @@ -255,12 +328,7 @@ static int read_tfra(struct Tracks *tracks, int start_index, AVIOContext *f)
>          goto fail;
>      }
>      // The duration here is always the difference between consecutive
> -    // start times and doesn't even try to read the actual duration of the
> -    // media fragments. This is what other smooth streaming tools tend to
> -    // do too, but cannot express missing fragments, and the start times
> -    // may not match the stream metadata we get from libavformat. Correct
> -    // calculation would require parsing the tfxd atom (if present, it's
> -    // not mandatory) or parsing the full moof atoms separately.
> +    // start times.
>      for (i = 0; i < track->chunks; i++) {
>          if (version == 1) {
>              track->offsets[i].time   = avio_rb64(f);
> @@ -283,6 +351,15 @@ static int read_tfra(struct Tracks *tracks, int start_index, AVIOContext *f)
>          track->offsets[track->chunks - 1].duration = track->offsets[0].time +
>                                                       track->duration -
>                                                       track->offsets[track->chunks - 1].time;
> +    }
> +    // Now try and read the actual durations from the trun sample data.
> +    for (i = 0; i < track->chunks; i++) {
> +        int64_t duration = read_moof_duration(f, track->offsets[i].offset);
> +        if (duration > 0) {
> +            track->offsets[i].duration = duration;
> +        }
> +    }
> +    if (track->chunks > 0) {
>          if (track->offsets[track->chunks - 1].duration <= 0) {
>              fprintf(stderr, "Calculated last chunk duration for track %d "
>                      "was non-positive (%"PRId64"), probably due to missing "
> @@ -576,11 +653,8 @@ static void print_track_chunks(FILE *out, struct Tracks *tracks, int main,
>          }
>          fprintf(out, "\t\t<c n=\"%d\" d=\"%"PRId64"\" ",
>                  i, track->offsets[i].duration);
> -        if (pos != track->offsets[i].time) {
> -            // With the current logic for calculation of durations from
> -            // chunk start times, this branch can only be hit on the first
> -            // chunk - but that's still useful and this will keep working
> -            // if the duration calculation is improved.
> +        if (abs(pos - track->offsets[i].time) > 3) {
> +            // 3 allows for t to drift a few units, e.g., for 1/3 durations
>              fprintf(out, "t=\"%"PRId64"\" ", track->offsets[i].time);
>              pos = track->offsets[i].time;
>          }

Martin rightly says that this is wrong: we must not fuzz the segment
start times, as they must match between the playlist and the generated
files. I'll change to fuzz the duration instead. BRB.

> --
> 1.9.3 (Apple Git-50)
>